André F.S. Amaral, of the Spanish National Cancer Research Centre in Madrid, and colleagues used data from seven epidemiologic studies published before March 2010 to examine the association between levels of selenium, as measured in serum and toenails, and bladder cancer. The risks were reported in meta-odds ratios (mORs).

The researchers found that the overall risk of bladder cancer for the highest compared with the lowest selenium status was decreased by 39 percent. Gender differences in risk were found, with selenium affording females (mOR, 0.55) relatively more protection from bladder cancer than men (mOR, 0.95). The authors concluded that gender-specific differences in the accumulation and excretion of selenium may exist, and that more large studies are needed to support these preliminary findings.

"In conclusion, this meta-analysis supports an inverse association between selenium concentration and bladder cancer risk. To further elucidate this relationship, efforts to quantify selenium and other trace metals in biological sample specimens at the individual level in large observational studies or randomized trials are needed. These are fundamental steps before suggesting selenium supplementation to bladder cancer patients," the authors write.